Hesperidin is a substance having the following chemical structure:

It is reported that hesperidin has effects of strengthening capillaries to reduce blood vessel permeability, effects of improving blood cholesterol and blood flow, antiallergic effects, cancer inhibition effects, etc. It is known that such excellent effects can be obtained, for example, when hesperidin is applied or orally taken.
However, hesperidin is extremely unstable in hesperidin-containing compositions, and gradually decomposes in the compositions.
Further, hesperidin is a substance with very low solubility; although it dissolves in strong alkali solutions having a pH of 11 or more, it barely dissolves in neutral to acidic solutions. For this reason, it is very difficult to obtain non-strong alkali solutions containing dissolved hesperidin to use them as foods, drugs, etc.; or use them for producing foods, drugs, etc. Furthermore, even when hesperidin is dissolved in a strong alkali solution, it is unstable and decomposed during long (e.g., several weeks) storage. Thus, hesperidin has very low stability.
An oral composition containing hesperidin is particularly expected to have an effect of maintaining the health of oral tissues by promoting the blood flow of the oral tissues; however, since the use of strong alkali solutions or strong alkali substances in the mouth damages oral tissues, it is difficult to produce and provide oral compositions that stably contain hesperidin on an industrial scale.
Under such circumstances, studies have been made to improve the stability of hesperidin in hesperidin-containing compositions. Various attempts have been made to increase the solubility of hesperidin in slightly alkaline to acidic solutions (for example, solutions having a pH of about 3 to 10).
For example, there are reports on a method comprising combining D-glucose with hesperidin to form α-glycosyl hesperidin, thereby increasing the solubility of hesperidin, and a method comprising forming an amorphous composition that contains hesperidin and a glucose adduct of hesperidin (in which glucose is attached to hesperidin) at a specific ratio, thereby improving the water solubility of hesperidin (Patent Literatures 1 and 2). However, production of glucose adducts of hesperidin is expensive; there is a problem in view of cost.
There are also reports on a method comprising dissolving hesperidin in a strong alkali solution, and then adding a polysaccharide thickener thereto to adjust the pH of the solution (Patent Literature 3). However, this method has a problem in view of stability, because hesperidin is extremely unstable, especially against light and oxygen in the alkali pH range, and impurities and crystals are gradually deposited when the pH is returned to a neutral level. Further, even when hesperidin is dissolved in strong alkali, there is a problem of decomposition during storage.
Therefore, it has been difficult thus far to suppress the decomposition of hesperidin in hesperidin-containing compositions. In particular, suppressing the decomposition of hesperidin and stably containing hesperidin in non-strong alkali solutions (e.g., solutions having a pH about 3 to 10) without using glucose adducts of hesperidin are difficult, and dissolving hesperidin is also difficult. For this reason, it is difficult to produce and supply hesperidin-containing compositions on an industrial scale.